Composite reinforcement elements woven in three dimensions

ABSTRACT

A composite reinforcement element comprising three superimposed and crossed even layers of threads and a continuous thread extending perpendicularly through the three superimposed even layers. The layers are impregnated with a binder and the binder is polymerized after impregnation. The superimposed and crossed even layers are initially maintained assembled, before the impregnation and the polymerization of the binder, by a conjugate action of gripping and friction of the three superposed and crossed even layers of threads on the continuous thread which extends therethrough. The continuous thread forms an internal surface of the composite reinforcement element which protrudes from the superimposed and crossed even layers of threads in the form of open loops which are interconnected on an external surface of the element.

This is a continuation of application Ser. No. 173,754 filed Mar. 22,1988, now U.S. Pat. No. 4,917,756.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to the manufacture of compositereinforcement elements woven or knitted in three dimensions fromtextile, mineral, synthetic or other fibers impregnated with a resinwhich is subsequently polymerized or otherwise hardened.

Reinforcement elements of this type are principally, but notexclusively, employed in the aeronautic and space fields in which theyhave many applications, in particular for producing parts which mustwithstand thermo-mechanical stresses, as the thermal protections ofbodies which re-enter the atmosphere, the powder rocket nozzles,aircraft brakes, or parts which must withstand high mechanical stressessuch as hubs of helicopter rotors, undercarriages and inserts of wings,leading edges, etc.

Many processes and apparatus have been imagined and developed forproducing such reinforcement elements, but the automatized manufactureof parts of complex shape encounters great difficulties which result invery complicated and consequently costly machines without the partsobtained always possessing all the required qualities of homogeneity andresistance.

Furthermore, the remarkable properties of these composite elements leadto the use thereof for constructing parts having complicated, evolutiveshapes that present machines are incapable of manufacturing.

Machines are known for producing composite reinforcement elements whichare of revolution, hollow and woven in two dimensions horizontallyaround rigid perpendicular rods mounted in concentric ring arrangementson a rotatable support, which are subsequently replaced by threads, asdescribed for example in US-A-4,183,232 and US-A-4,346,741 in the nameof the applicant.

According to another method, a hollow support mandrel is used on thesurface of which a plurality of parallel layers of threads is depositedin two crossed directions and lines of stitching perpendicular to theselayers are formed, as described in particular in FR-A-2,355,936.

According to FR-A-2,315,562, the hollow support mandrel is of metal andcapable of being taken apart and formed by spaced sectors comprisingapertures in which points are driven, around which points are stretchedout threads forming the various crossed superimposed layers which arethereafter sewn by rows of stitches formed in the gaps between thesectors of the mandrel.

All the processes and apparatus described in these documents require ahollow mandrel since the connection of the superimposed layers bystitches necessarily requires introduction of a device in the mandrelfor knotting the thread introduced from the exterior.

Moreover, the stitches are effected with needles having a flap valve ora closed eye which is delicate to use for fragile fibers which sometimesrequire a lapping of the thread.

Another process and device described in FR-A-2,408,676 employ on theother hand a solid mandrel composed of foam material in which sectionsof rigid threads, termed "picots", are implanted and around which thelayers of threads are laid in two different directions and whichconstitute the threads of the third direction.

This process has various drawbacks. First of all, the "picots" must bepreviously subjected to a pre-rigidifying treatment, which increasestheir diameter, to permit their implantation.

Secondly, the "picots" which must become an integral part of the part tobe produced must consequently be provided in a considerable number, onthe order of several tens of thousands, implanted very close to oneanother, which is practically impossible with a machine.

Furthermore, in the case of a part having a complex shape whose surfaceforms corners or curves, the implantation of the neighboring "picots"which are excessively close together is very difficult to achievewithout interference therebetween, and the very narrow passages theydefine do not permit an easy laying of the threads in even layers, whichlaying is found to be even impossible in the regions where the threadschange orientation.

Lastly, the "picots" excessively close to one another behaveimperfectly, in particular in the curved parts, and this results indefective homogeneity in the finished part.

SUMMARY AND OBJECTS OF THE INVENTION

An object of the invention is to overcome these drawbacks and those ofthe other processes and devices of the prior art, by providing a novelmachine whereby it is possible to produce reinforcement elements whichnot only have the shape of a solid of revolution but also an evolutiveprofile (large variations in diameter and curvature) and shapes havingflat surfaces or even flat shapes or blocks.

The invention provides a machine for carrying out a process formanufacturing composite reinforcement elements woven in three dimensionsfrom textile, mineral, synthetic or other fibers, which have complexshapes, a high resistance to thermal, mechanical or thermo-mechanicalstresses, and intended more particularly for applications in theaeronautic or space field, the process being of the type comprisingemploying a disposable mandrel composed of a foam or like materialhaving externally the internal shape of the reinforcement element to beproduced, implanting rigid members in the mandrel and applying on thesurface of the mandrel successive layers of threads or fibers, whichlayers are superimposed and crossed in at least two directions,interconnecting said layers by means of threads or fibers which extendperpendicularly therethrough impregnating the assembly with a hardenablebinder, and withdrawing the mandrel, said rigid members being pinstemporarily implanted in the mandrel for retaining a continuous threadof fibers on said pins and in contact with the surface of the mandrel,stretching out a continuous thread on said pins so as to form insuccession at least three superimposed and crossed even layers,introducing through said layers from the exterior a continuous threadforming successive open loops by means of a needle through which saidthread passes, and withdrawing said pins.

In a reinforcement element produced in this way, said layers aremaintained assembled by conjugate gripping and friction actions of thethreads of said layers on said thread loops.

The machine according to the invention is of the type comprising aframe, a horizontal rotatable mandrel-carrying shaft, a detachablemandrel composed of a perforatable material mounted on said shaft, andmeans for driving said shaft in rotation, wherein the frame carries avertical arm which is located above said shaft and adjustable alongthree orthogonal axes and includes at its lower end fixing means fordetachable work devices and means for orienting said device about ahorizontal axis.

According to another feature of the invention, a set of three differentdetachable work devices is provided which are adaptable on said lowerend of the arm, namely a device for driving the pins into the mandrel, adevice for laying thread and a needle device for driving in a continuousthread forming consecutive loops through the crossed layers of threadlaid on the mandrel.

Another object of the invention is to provide a product produced by theprocess and machine defined hereinbefore, said product comprising atleast three crossed and superimposed even layers of threads of fibersmaintained assembled by a gripping and friction action on theconsecutive loops of a continuous thread introduced from the exteriorthrough said layers by means of a hollow needle.

The following description with reference to the accompanying drawingsgiven by way of non-limitative examples will explain how the inventioncan be carried out.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of the machine accordingto the invention.

FIG. 2 is a longitudinal sectional view of the end of themandrel-carrying shaft and a mandrel composed of a foam materialdisposed on this shaft.

FIG. 3 is a perspective view of an embodiment of a reinforcement elementin process of being manufactured, showing the arrangement of the pinsimplanted in the mandrel and the arrangement of the thread on thesepins.

FIG. 4 is a partial perspective view of a first detachable work deviceadapted to implant pins in the mandrel and mounted on the lower end ofthe vertical arm.

FIGS. 5 and 6 are views to an enlarged scale of another detachable workdevice adapted to lay the thread on the mandrel, mounted at the lowerend of the vertical arm, and means for orienting the thread layingdevice.

FIG. 7 is a view to an enlarged scale of the needle work device adaptedto introduce continuous thread loops through the layers disposed on themandrel.

FIG. 8 is a longitudinal sectional view to an enlarged scale of theneedle employed in the work device of FIG. 7.

FIG. 9 is a longitudinal sectional view of a modification of the needle.

FIGS. 10a to 10f are diagrammatic sectional views of the differentstages of the introduction of the loops of continuous thread through thelayers laid on the surface of the mandrel.

FIG. 11 is a longitudinal sectional view of the finished reinforcementelement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1, the machine according to the inventioncomprises a frame having two feet 1, a lower cross-member 2, twovertical posts 3 interconnected in their upper part by a secondcross-member 4 and two lateral supports 5.

Each vertical post 3 comprises a slideway 6, and a transverse bar 7 isfixed in the vicinity of its ends in slides 8 slidably mounted in theslideway 6, in which latter they can be immobilized by screws 9. Withthis arrangement, the bar 7 can be adjusted in height on the posts 3.

Mounted on the bar 7 is a carriage 10 on which is mounted a horizontalarm 11 transversely slidable in an adjustable manner relative to the bar7.

The horizontal arm 11 carries at one of its ends a vertical arm 12 alsoslidably mounted in an adjustable manner.

The vertical arm 12 includes at its lower end 13 fixing means adapted toreceive a detachable work device which is more clearly shown in FIGS. 4to 7.

The machine further comprises a horizontal shaft 14 rotatably mounted inone of the lateral supports 5 and adapted to carry a mandrel 15, thisshaft extending in a direction parallel to the bar 7 and below thelatter.

The shaft 14 is driven in rotation by a step-by-step electric motor 16which is also mounted on the lateral support 5.

It will be understood that, owing to the arrangement of the bar 7 andthe arms 11 and 12, the end 13 may be adjusted in any desired positionwith respect to the mandrel 15 along three orthogonal axes X, Y and Z bymeans of motors M1, M2 and M3 which are shown by way of example to bemounted on the bar 7 and at the ends of the arms 11 and 12 and to drivethe latter along said three axes through suitable known systems such asa rack and pinion system, lead-screw system or other system.

With reference more particularly to FIGS. 5 and 6, the lower end 13 ofthe arm 12 comprises a foot 17 fixed in the extension of the arm and onwhich is fixed a small electric motor 18, for example a step-by-stepmotor, whose horizontal shaft 19 extends through the foot 17.

FIG. 4 shows a first work device designated by the reference numeral 20which maY be detachably mounted on the shaft 19 of the motor 18.

This device 20 is a pneumatic nailing device of known type comprising adouble-acting jack 21 connected through pipes 22 to a source ofcompressed air and to a control (not shown) and a vibratoryreservoir-box 23 containing pins and connected to the device 20 througha pipe 24.

The reservoir 23 may be mounted on the frame of the machine or onanother suitable support (not shown).

Mounting the device 20 on the shaft of the motor 18 enables this deviceto be oriented at any angle in a vertical plane and enables pins 25 tobe driven in at all the desired points on the surface of the mandrel 15.

FIGS. 5 and 6 show a second work device which may be detachably mountedon the shaft 19 of the motor 18.

This second work device, designated by the reference numeral 26, isadapted to lay a thread on the surface of the mandrel 15 between thepins 25 or around the latter.

For this purpose, the device 26 comprises a support 27 adapted to belocked on the shaft 19 by a locking screw 28.

This support 27 carries a small step-by-step electric motor 29 whoseshaft 30 extends vertically downwardly and carries a thread guide formedby a tube 31 of flattened sectional shape, open at the lower end anddefining an opening 32 in its upper part, a thread 33 to be laid on themandrel entering the thread guide tube 31 through the opening 32 andissuing therefrom at the lower end.

This lower end of the tube 31 is internally rounded as shown at 34 toavoid any risk of damage to the thread in the case of a fragile thread,and breakage of the latter when it issues from the thread guide tube 31at a pronounced angle to the latter.

The thread 33 comes from a reserve 35 of reels mounted on the frame orother suitable support.

FIG. 7 shows a third work device adapted to introduce loops of acontinuous thread through layers previously laid on the surface of themandrel 15.

This device, designated by the reference numeral 36, may also bedetachably mounted on the shaft 19 of the motor 18. It comprises asupport 37 fixed to the shaft 19 on which a rail 38 is fixed, a block 39being slidable in the rail 38, and a pneumatic jack 40 has its cylinderfixed on an extension 41 of the rail 38, which extension is rigid withthe rail, while the piston rod 42 of the jack is connected to the block39.

The block 39 carries a needle 43 which is shown in section to anenlarged scale in FIG. 8 and will be described in more detailhereinafter.

The end 47 of the needle remote from its point 46 is fixed to one sideof a pneumatic thread-clamp 48 of known type mounted on the block 39.

The thread-clamp 48 is connected through pipes 49 to a source ofcompressed air (not shown) and a thread of fibers 50 coming from asource (not shown) extends through the thread-clamp 48 and the passage44 of the needle 43 and issues from the latter through the eye 45.

A return spring 52 is advantageously provided between the block 39 andthe rail 38 so that, when the jack 40, fed with fluid through a pipe 53,has urged the block 39 forwardly in extension and is then connected toexhaust, the spring 52 returns the block 39 and the needle rearwardly.

It will be observed that the device 36, as the device 20, may beoriented in a vertical plane by the motor 18.

According to the process of the invention, the first work device 20 isemployed in a first stage, this device being mounted on the end of thearm 12 of the machine, for implanting the pins 25 in the mandrel 15composed of foam material at points of the surface of the mandrel chosenas a function of its shape, for retaining and maintaining a thread 33against the surface of the mandrel between these pins and thus form aneven layer.

In the embodiment represented in FIG. 2, the mandrel has acylindro-conical shape corresponding to the inner shape of thereinforcement element to be produced.

There is implanted, for example, a first series of pins 25a around theshaft 14, on the roughly flat part of the mandrel. There are thenimplanted, for example, two circumferential rows of pins 25b at the endsof the cylindrical body of the mandrel, then pins 25c spaced apart instaggered relation on the conical end part of the mandrel, pins 25d atthe apex of this end part and finally pins 25e in circumferential rowsin the parts of the surface of the mandrel which are inclined relativeto its shaft 14.

Note that the pins 25b and all those implanted in the surfaces of themandrel parallel or substantially parallel to its shaft areperpendicular to its surface, while the pins 25a, 25c, 25d and 25e, andgenerally all those implanted in surfaces which are inclined andperpendicular to this shaft will be advantageously inclined in thedesired direction so that the thread tends to slide therealong andbecomes lodged in an acute-angled corner formed by each of these pinswith the associated surface of the mandrel.

In order to effect these implantations, the device 20 is shiftedlongitudinally along the surface of the mandrel 15 by inclining thedevice 20 in a suitable manner by actuating the motor 18 and by rotatingthe mandrel one step after each travel of the device 20 by means of themotor 16.

When pins have been implanted at all the chosen points, the device 20 isreplaced by the device 26. A thread 33 is passed through the opening 32in the thread guide 31, with the end of the thread issuing at the lowerend of the thread guide.

This end is fixed, for example on one of the pins 25a, and the device 26is shifted in the same way as in the preceding operation, by drawing thethread between the pins 25b to a point beyond one of the pins 25d at theapex of the cone.

The mandrel is then turned through one step and the thread 33 is broughtback by passing it around the pin 25d, between two pins 25b, then, byinclining and lowering the device 26, by passing it around in the sameway a second pin 25a adjacent to that of the start of the operation.

In order to avoid an accumulation of thread in the vicinity of the apexof the cone, intermediate pins 25c, spaced apart in staggered relationon the cone, are passed around.

When a first even layer of thread 33 has been in this way laid in thelongitudinal direction, a second layer of thread is laid for example at90° in the circumferential direction.

This winding may be carried out in a helical manner from, for example,one of the pins 25a by turning the mandrel and shifting the device 26 ina linear path.

The circumferential rows of suitably inclined pins 25e are adapted toreceive a thread and to retain the thread in contact with the roughlyplanar end surface of the mandrel, and on its rounded part up to thestart of the cylindrical part.

Likewise, the circumferential rows of pins 25e on the conical part areadapted to prevent the thread from sliding toward the apex.

Lastly, the pins 25b implanted in the parts of the surface parallel tothe shaft of the mandrel are adapted to maintain an even spacing of thethreads, and the thread guide 31 can be turned around its axis by themotor 29 for the purpose of presenting its narrowest section between therows of pins.

The desired number of superimposed layers are in this way laid on themandrel and it will be observed that if it is desired to reinforce anypart of the element, it is sufficient, in the first stage, to implantpins at the boundaries of this part which will permit one or moreadditional passes of thread laying between these pins to be effected bypassing therearound in one direction and then the other.

It must be stressed that, in the case of an evolutive surface having forexample a concave part, there may be implanted, in the first stage,helical rows of pins against which the thread 33 is laid.

When this second stage of manufacture has terminated, the device 26 isreplaced by the third work device 36.

The thread 50 is threaded through the thread-clamp 48 and passes alongthe needle 43 and, in a third stage, this thread is introduced throughthe crossed layers laid on the mandrel.

The thread 50 is introduced in the form of free loops by the needle 43urged forwardly by the jack 40 and returned by the spring 52 inaccordance with the sequence shown in FIGS. 10a to 10f, therebyeffecting successive stitches.

The thread 50 is driven by the needle 43 through the layers, thethread-clamp being in the clamping position, and the travel of theneedle being so adjusted as to penetrate the foam material of themandrel to an extent a little beyond the eye 45 of the needle (FIGS.10a, 10b, 10c).

The thread-clamp is then released (FIG. 10d) and the needle risesreleases the thread progressively (FIG. 10e) through the layers and thusforms a small unclosed loop 53 which is solely retained by the foam andthe friction in the layers, down to below the interface between the foamand the first layer.

It will be understood that the elastic pressure of the foam materialclosing onto the loop after the withdrawal of the needle, on one hand,and the friction and gripping action of the threads of the superimposedlayers, on the other hand, when the needle is withdrawn, are sufficientto retain the thread 50 which freely travels through the passage of theneedle during this withdrawal.

After having travelled out of the layers of thread, the needle is madeto rise above the surface of the layers a distance equal to the totalthickness of the superimposed layers on the mandrel plus the stitchpitch, i.e. the desired spacing between two stitches (FIG. 10f).

The thread-clamp is then actuated for blocking the thread in the needle,the arm 12 is shifted one step, and the device is again brought intoaction for recommencing the cycle and thus continuously forms a largenumber of loops 53 with the same thread 50.

The pins implanted in the mandrel may be withdrawn progressively as thework of the device 36 progresses so as to avoid hindering itsprogression.

The shape of the needle is of great importance for effecting this thirdstage. Indeed, the threads 50 employed are most often threads havingfragile fibers which may tend to separate from one another.

Consequently, it has been observed that if a needle having aconventional throughway eye is used, the fibers of the thread come apartat the outlet of the eye on both sides of the latter which results incramming and breakage of the thread.

For this reason, and as shown in FIG. 8, the needle 43 has an obliquethroughway eye 45 whose edge remote from the point 46 has an innerrounded portion 51 around which the thread is bent upon penetration ofthe needle, thereby avoiding damage to the thread, or a splitting liableto cause its breakage.

The throughway eye 45 advantageously opens, at its end remote from thepoint 46, onto a longitudinal groove 44 of partly circular section whosedepth gradually decreases in a direction away from the point and inwhich the thread travels.

In the embodiment shown in FIG. 9, the needle 43a is hollow and definesan axial passage 44a which opens laterally and obliquely onto anon-throughway eye 45a whose edge remote from the point 46a has an innerrounded portion 51a similar to the rounded portion 51 of the needle 43,and the thread travels through the interior of the needle.

It will be understood that, with the machine according to the invention,the operation of the device 36 may be very rapid with a very regular oreven pitch on all the parts of the surface of the mandrel by orientingthe whole of the device 36 in a suitable manner for each of the parts ofthis surface.

Thus, in the end region remote from the apex of the conical part of themandrel, the inclination of the device 36 will be gradually increased sothat the needle passes through the layers always perpendicularly to thelatter.

It will also be understood that the motors M1, M2, M3, 18, 29 and 16 aresuitably controlled for effecting all these operations by means of anelectronic device which includes a memory and is previously suitablyprogrammed in accordance with the shape of the element to be produced,this device being of known type and not being part of the invention.

When the operation for introducing threads through the layers hasterminated, the assembly is impregnated, either by leaving thereinforcement element on the mandrel or by previously withdrawing thelatter in accordance with the conventional method.

In this respect, the essential feature of the element produced inaccordance with the invention should be stressed, namely the fact thatthe superimposed and crossed layers of threads are maintained assembled,before impregnation, merely by the conjugate actions of the gripping andthe friction of the threads of the superimposed layers on the continuousthread which passes therethrough in forming successive open loopsinterconnected on the outer surface of the element.

The applicant has found that these gripping and friction effects arealone sufficient to permit a reinforcement element produced in this wayaccording to the invention to be handled and to retain its shape afterthe withdrawal of the mandrel and before its impregnation. It will beunderstood that such a result can only be obtained with at least threecrossed superimposed layers.

For withdrawing the mandrel, the simplest procedure is to destroy it,for example by combustion.

FIG. 11 shows the shape of the finished element and reveals thearrangement of the threads in three dimensions.

The use of temporary pins according to the invention requires theimplantation of only a few hundred thereof for laying the layers on agiven element, whereas the use of picots of the prior art requires theimplantation of several tens of thousands thereof as definitive threadson the same element.

Consequently, the larger space left free between the pins permits thelaying of denser layers of threads, these threads being moreover stillfurther tightened by the introduction of the threads by means of theneedle.

An element results whose properties of resistance are greatly superiorto those of the elements of the prior art.

I claim:
 1. A composite reinforcement element of complex evolutive shapewoven in three dimensions and at least three directions, comprising atleast three superimposed and crossed even layers of threads, and acontinuous thread extending perpendicularly through said layers, saidlayers being impregnated with a binder, said binder being polymerizedafter impregnation, wherein said layers are initially maintainedassembled, before the impregnation and the polymerization of the binder,merely by a conjugate action of gripping and friction of the threads ofthe layers on said continuous thread which extends therethrough andwhich forms on an internal surface of the element successive protrudingopen loops which are interconnected on the external surface of theelement, said continuous thread being maintained in position solely byfrictional forces.
 2. A composite reinforcement element formed by thesteps of: employing a disposable mandrel composed of foam, said mandrelhaving an external surface, said mandrel external surface correspondingto an internal surface of the reinforcement element to be produced;implanting rigid pin members in the mandrel; applying successive layersof threads on the surface of the mandrel stretched out between saidrigid pin members, said threads being superimposed and crossed in atleast two directions; interconnecting said layers of threads by means ofa continuous thread extending substantially perpendicularly through saidlayers by driving a needle carrying said continuous thread through saidlayers and into the mandrel such that an eye of the needle fullypenetrates the external surface of the mandrel said continuous threadforming successive open loops protruding from said internal surface ofthe reinforcement element and protruding into the foam material of themandrel, said continuous thread being held in place solely by africtional effect from engagement with said foam material; impregnatingsaid layers of threads and said continuous thread with a binder;hardening said binder after impregnation; withdrawing the pins andremoving the mandrel.
 3. A composite reinforcement element according toclaim 2, wherein said continuous thread is introduced through saidlayers of threads by means of a needle having a throughway eye having anedge defining an internal rounded portion and a longitudinal groovewhich opens laterally and obliquely onto the eye.
 4. A compositereinforcement element according to claim 2, wherein said needleintroducing said continuous thread through said layers comprises anon-throughway eye having an edge defining an internal rounded portionand an axial passage opening laterally and obliquely onto the eye.
 5. Acomposite reinforcement element having a complex evolutive shapeincluding threads woven in three dimensions extending in at least threedirections, said threads woven in three dimensions comprising threelayers of threads superimposed and crossed on a form having said complexevolute shape said form having an external surface corresponding to aninternal surface of said reinforcement element a continuous threadextending substantially perpendicularly through said three layers andthrough said complex evolute shape said at least three superimposedlayers and said substantially perpendicularly extending continuousthread being impregnated with a binder which is thereafter polymerized,said three layers and said continuous tread being maintained in anassembled position, prior to being impregnated with said binder, saidcontinuous thread forming successive open loops protruding through saidexternal surface, said continuous thread being held in place by frictionof contact with said three layers and said form said loops beinginterconnected on the external surface of the element.
 6. A compositereinforcement element, comprising three layers of superposed and crossedthreads positioned on a mandrel having an external surface correspondingto an internal surface of the three superimposed and crossed layers ofthread; a continuous thread extending substantially perpendicularlythrough said three layers of superposed and crossed threads, saidcontinuous thread defining closed loops extending across ones of saidsuperimposed and crossed threads at an external side of saidsuperimposed and crossed threads and forming open loops, not extendingacross ones of said three layers of superimposed and crossed threads, atan internal side of said three layers of superimposed and crossedthreads, said open loops protruding out from said internal surface, saidthree layers of superimposed and crossed threads being impregnated witha binder which is thereafter polymerized, said layers being maintainedin an assembled position, prior to being impregnated with said binder,solely by the friction of the three layers and the mandrel.